1. Field of the Invention
The present invention relates to a method for producing a welded crankshaft having a plurality of individual parts and a production line for carrying out the method. The welded crankshaft has no heat-affected zone (HAZ) in the sections that were welded and little or no dimensional distortion such that the welded crankshaft has substantially similar or improved mechanical and impact properties as a solid crankshaft.
2. Description of Related Art
Crankshafts may be manufactured from a plurality of component parts that are welded together. Generally, the welding occurs between the ends of the journal and the web, or within the journals themselves. As is known in the art, the heat from the welding process creates a HAZ in the basis metal in the area adjacent to the weld. The creation of this HAZ has adverse metallurgical effects on the basis metal and, thus the welded component. Such effects include the creation of notch effects and/or grain reduction in impact properties, which cause a weakening of the metal in the HAZ. This can lead to failures that limit the useful life of the welded crankshaft. Post-weld heat treatment (PWHT) has been used to eliminate the HAZ. However, PWHT can lead to deformation and dimensional distortion of the finished product.
Several patents have been directed to welded crankshafts and welding processes that reduce or eliminate the HAZ.
U.S. Pat. No. 2,403,049 is directed to a method of making crankshafts by welding together forged components comprising a web with a stub on each side. The stubs of multiple components are electric welded together followed by a stress-relieving heat treatment where the crankshaft is placed in a complicated jig to reduce dimensional distortion.
U.S. Pat. No. 2,583,362 is directed to a method and apparatus for induction or pressure butt welding components of a crankshaft in a protective atmosphere to prevent oxidization and cause carburization of the welded surfaces. Based on the described method, the metallurgical quality of the crankshaft would be closer to a cast crankshaft than a wholly forged crankshaft.
U.S. Pat. No. 2,678,370 directed to a method and means for heating metallic objects to an even and uniform welding temperature prior to pressure butt welding. The method uses electrical currents to provide heating in areas remote from an external heating source. The electrical currents take advantage of the variation in the resistivity of the metal as a function of temperature to uniformly heat the metallic object in the areas where the convective heating from the external source is reduced.
U.S. Pat. No. 3,144,702 is directed to method for a manufacturing a crankshaft using components comprising a web with a pin shaped extension on each side. A tube of wear-resistant material is placed over the pins and the corresponding pins cm two components are welded together, preferably by flash butt welding.
U.S. Pat. No. 4,008,927 is directed to a welded crankshaft manufactured from components having a crankshaft section having an end face and a main shaft journal section having an end face. The end faces of the crankshaft sections of the components and the main shaft sections of the components are electron beam welded together after centering pins have been placed in the end faces of the sections to align them for welding.
U.S. Pat. No. 5,303,468 is directed to a welded crankshaft where tubular journals are electron beam welded at their ends to a web. An angled surface on the end of the journal and a corresponding groove in the web facilitate the electron beam welding process. The HAZ created by electron beam welding is expected to be smaller than the HAZ created by induction or other welding methods, but not eliminated.
U.S. Pat. No. 6,378,396 describes a crankshaft manufactured from individual components having a web with tubular segments disposed on each side. The tubular segments are friction welded together to form the crankshaft.
United States Patent Application Publication No. 2006/0086708 is directed to a method for welding together two metallic pieces in order to eliminate the need for PWHT after welding to eliminate the HAZ. The method comprises overlay welding the surfaces to be joined with a nickel-based filler metal, heat treating to eliminate or temper the HAZ created by the overlay welding process, and then welding the overlaid surfaces of the two metallic pieces together using a nickel-based filler metal.
United States Patent Application Publication No. 2006/0191878 is directed to a welding method where the surfaces to be welded are plastically deformed and then machined prior to welding.
None of this prior art provides a method for manufacturing a welded crankshaft having no HAZ without the use of a PWHT that can cause distortion. It has been found that by upset forging the welded portion of the crankshaft, the HAZ is eliminated and little or no distortion of the resulting crankshaft section occurs.